From R. de Werdt et al, IEDM 1987, pp. 532-535, a method of the kind set forth is known where an n-type semiconductor region and a p-type semiconductor region are formed adjacently after the formation of field oxide regions. These semiconductor regions extend partly underneath field oxide regions where they adjoin one another. For the formation of these regions an implantation with an n-type dopant and an implantation with a p-type dopant are carried out with such a high implantation energy that a maximum doping concentration is obtained just underneath the field oxide regions. The semiconductor regions thus formed are referred to as an n-well and a p-well, respectively. The highly doped parts of the semiconductor regions which are situated just underneath the field oxide regions enhance the insulating effect of the field oxide regions; these parts are also referred to as channel stoppers. In the n-well a p-channel MOS transistor is formed; in the p-well an n-channel MOS transistor is formed. In order to ensure that these transistors obtain suitable properties, a further implantation with dopants is performed in the n-well as well as in the p-well. This further implantation serves to impart a suitable high breakdown strength to the transistors and is also referred as an anti-punch-through implantation.